obscenity

Members of the USgovernment are famous for saying "I can't define it, but I know it when I see it." Unfortunately, if they can't define it, then we can't make it illegal because the laws become methods of censorship, as one person's obscenity is another person's art or free speech.

obscenity: imagery, ideation, narratives and other representations and actualities which offend and disgust the sensibilities of the perceiver. Imprecisely, the term is used to refer to sexually explicit material or media (SEM), including pornography, and also sexual actions or utterances that are traditionally classified as forbidden. As in erotica, what is perceived as obscene is usually idiosyncratic and is incongruent with the specifications of one's lovemap. See also erotica; lovemap; pornography; sexually explicit media.

That quality in words or things which presents what is offensive to chasity or purity of mind; obscene or impure lanquage or acts; moral impurity; lewdness; obsceneness; as, the obscenity of a speech, or a picture.

Mr.Cowley asserts plainly, that obscenity has no place in wit.
Dryden.